DNA methylation in the androgen receptor gene promoter region in rat prostate cancers

BACKGROUND Invasive adenocarcinomas developing in the rat dorsolateral prostate on combined treatment with 3,2′‐dimethyl‐4‐aminobiphenyl (DMAB) and testosterone propionate (TP) are biologically androgen‐independent and lacking androgen receptor protein (AR) expression. The present study was conducted to assess the mechanisms underlying this loss of AR expression in rat prostate cancer. METHODS The methylation status of the AR gene promoter region in rat prostate cancer and cell lines (PLS10, 20, and 30) was examined by Southern blotting, methylation‐specific polymerase chain reaction, and methylation‐sensitive single‐strand conformation analysis (MS‐SSCA). RESULTS AR mRNA expression was not detected in any of the rat prostate cancers or cancer cell lines tested by Northern blot analysis. Higher levels of methylated CpGs were observed in PLS20 than PLS10 or 30. Demethylation treatment by 5‐aza‐2′‐deoxycytidine restored AR mRNA expression in PLS20. The CpGs suggested to be responsible for AR expression in rat prostate cancer were found to be located ‐9 and ‐1 nucleotides upstream of the transcriptional initiation site. All of the examined rat prostate and seminal vesicle cancers demonstrated hypermethylation at these CpG sites. CONCLUSIONS These data clearly demonstrate that aberrant hypermethylation in the AR promoter region may play a critical role in AR expression in rat prostate cancers. Prostate 52: 82–88, 2002. © 2002 Wiley‐Liss, Inc.